Categories page: descriptions, per-category terminal illustrations, full ZH version

- 7 categories now listed with name, blurb, post count and a
  per-category terminal-style SVG illustration (CategoryArt)
- empty categories show '0 posts · coming soon' (non-link, no soft-404)
- new zh pages: /zh/categories/ index + /zh/categories/[category]/ detail
- PostList is locale-aware (zh-CN dates, zh category links)
- zh nav '分类' now points to /zh/categories/
- category detail pages get art + description header
- language switch wired both ways (EN <-> ZH)

src/components/PostList.astro

@@ -4,13 +4,23 @@ import type { CollectionEntry } from 'astro:content';
 interface Props {
   posts: CollectionEntry<'posts'>[];
   limit?: number;
+  lang?: 'en' | 'zh';
 }
 
-const { posts, limit } = Astro.props;
+const { posts, limit, lang = 'en' } = Astro.props;
 const shown = limit ? posts.slice(0, limit) : posts;
+const isZh = lang === 'zh';
 
 const fmt = (d: Date) =>
-  d.toLocaleDateString('en-US', { year: 'numeric', month: 'long', day: 'numeric' });
+  d.toLocaleDateString(isZh ? 'zh-CN' : 'en-US', {
+    year: 'numeric',
+    month: 'long',
+    day: 'numeric',
+  });
+
+const updatedLabel = isZh ? '更新于' : 'Updated';
+
+const catHref = (cat: string) => `/${isZh ? 'zh/categories' : 'categories'}/${cat}/`;
 
 const og = (post: CollectionEntry<'posts'>) => post.data.ogImage || '/og-default.png';
 ---
@@ -28,13 +38,13 @@ const og = (post: CollectionEntry<'posts'>) => post.data.ogImage || '/og-default
           {post.data.updatedDate && (
             <>
               <span class="sep">·</span>
-              <span class="updated" title={`Updated ${fmt(post.data.updatedDate)}`}>
-                Updated {fmt(post.data.updatedDate)}
+              <span class="updated" title={`${updatedLabel} ${fmt(post.data.updatedDate)}`}>
+                {updatedLabel} {fmt(post.data.updatedDate)}
               </span>
             </>
           )}
           <span class="sep">·</span>
-          <a class="tag" href={`/categories/${post.data.category}/`}>{post.data.category}</a>
+          <a class="tag" href={catHref(post.data.category)}>{post.data.category}</a>
           {post.data.tags.map((t) => <span class="tag">{t}</span>)}
         </div>
         <p>{post.data.description}</p>